In recent years, the control of shipped goods from one location to another has become more sophisticated and complex with increases in the number of consumers, and the distances between the consumers and most manufacturers. In addition, there has been an associated increase in the speed in which many goods need to be delivered. Also, the concept of "just in time" manufacturing and supply concepts have been developed which have necessitated the rapid supply of goods.
One major problem with the above shipping situation is that occasionally goods, or even loads of goods, become lost. Considering the amount of cargo traffic which traverses rail yards, cargo ships, truck depots, etc., one realizes the magnitude of the challenge to maintain effective shipping techniques without the associated losses. Even though most lost goods are eventually found, the searching process itself is inefficient and can severely impact manufacturing and supply schedules. Additionally, the searching process may take place under less than desirable or even hazardous conditions (in the winter, in the desert, etc.).
The present invention provides for a system by which the lost item (tractor trailers, rail cars, shipping containers, etc.) can be easily and quickly located. This system uses the known global positioning system (hereafter GPS) to assist in finding the lost object. The use of GPS to define the position of objects, by itself, is not new and has been used in the navigational positioning of airplanes, ships, etc. However, such GPS systems have used a relatively large amount of energy. Alternately, the use of individual GPS receivers located on each shipped item would make a system for locating a lost item from many similar items prohibitively expensive. Therefore, the present invention provides a technique by which a single GPS receiver can be used adjacent to a single stock area (or any location where there are likely to be lost articles) to reliably locate those lost articles. This is accomplished by positioning a translator in close proximity to the lost article, which alters the frequency of the GPS signal. The altered GPS signal and the GPS original signal are received by an interrogation unit, which compares the original and the translated signal to determine the relative position of the translator.
Prior systems for locating lost articles, where each article continually transmits a continuous GPS signal, not only produce a lot of needless congestion over the transmission networks, but also require each lost article to have a significant energy source. When the transmission to a distant satellite is required, as is the case in GPS systems, a large amount of energy is expended by the transmitters. Such a system would require either large generators or expensive batteries necessitating large expenses, frequent replacements, or recharging. Since none of the above options are attractive or practical, it is desirable to produce a power management portion which limits the energy expended by such transmissions, which forms one of the major aspects of the present invention.